Motion picture photographic film elements that are used as print films for movie theater projection have long used a carbon black-containing layer on the backside of the film. This backside layer provides both antihalation protection and antistatic properties prior to film processing. The carbon black is applied in an alkali-soluble binder that allows the layer to be removed by a process that involves soaking the film in alkali solution, scrubbing the backside layer, and rinsing with water. This carbon black removal process, which takes place prior to image development, is both tedious and environmentally undesirable since large quantities of water are utilized in this film processing step. In addition, in order to facilitate removal during film processing, the carbon black-containing layer is not highly adherent to the photographic film support and may dislodge during various film manufacturing operations such as film slitting and film perforating. Carbon black debris generated during these operations may become lodged on the photographic emulsion and cause image defects during subsequent exposure and film processing.
After removal of the carbon black-containing layer, antistatic properties provided thereby are lost. Undesired static charge build-up can then occur on processed motion picture print film when transported through projectors or on rewind equipment. While discharge of high static charges does not cause static marks on the processed photographic film as the film's light sensitive silver halide has also been removed during film processing, high static charges can attract dirt particles to the film surface. Once on the film surface, these dirt particles can create abrasion or scratches or, if sufficiently large, the dirt particles may be seen on the projected film image.
U.S. Pat. No. 5,679,505 describes a motion picture print film which, in place of a carbon black-containing layer on the backside of the film, contains an antihalation undercoat on the front side of the film support under the film emulsion layers, and an antistatic layer and a protective overcoat on the backside of the support. The protective overcoat is comprised of a polyurethane binder and lubricant. The polyurethane binder has a tensile elongation to break of at least 50% and a Young's modulus measured at 2% elongation of at least 50000 lb/in.sup.2. Despite the toughness of this overcoat, abrasive wear and the subsequent dust generation have continued to be a problem with protective overcoats in motion picture print film. During the lifetime of a print in a theater, abrasions in the perforation area can become severe enough that the soundtrack is damaged. In addition, dust can build up in the picture area of the film and reduce the quality of the projected image.
One approach that greatly reduces projector dust is to heavily lubricate the overcoat. However, at the lubricant levels necessary to reduce dusting in projectors, the coefficient of friction of the overcoat is reduced to the point that such a film is non-manufacturable because support rolls have insufficient traction for satisfactory conveyance in high speed sensitizing machines, and also because the long, slit rolls of photographic film become telescoped or dished in storage or shipping, wherein the roll integrity is at risk. It would be desirable to reduce projector dust by providing a print film with a highly lubricated protective overcoat having a sufficiently high coefficient of friction to eliminate the above manufacturing difficulties.